This invention relates to a process for producing a light control sheet equipped with a light scattering pervious region and a straightwardly light-advancing pervious region.
Conventional transparent bodies made of plastics or glass are transparent to light rays from any angle. As a structure which is pervious to light falling only from a specific angle, a "light-shielding plate" has generally been used which is composed of a relief forming lattices or fringes on a transparent substrate using an oriented film cut out from a plastic block obtained by alternately bonding a transparent plastic sheet and a non-transparent plastic sheet or from a photosensitive resin, and a transparent plate further combined on the relief. Such a light-shielding plate is proposed, for example, in Japanese Laid-Open Patent Publication No. 189489/1982.
Conventional oriented films or light-shielding plates are very costly because the manufacturing methods for them are very complex, and the oriented films alone do not give homogeneous film quality.
Japanese Laid-Open Patent Publication No. 40902/1989 discloses a method of producing a light control plate having the function of scattering light rays which are incident at a predetermined angle, which comprises maintaining a resin composition comprising at least two photopolymerizable oligomers or monomers having different refractive indices in film form, and irradiating light from a specific direction to the film-like resin composition to cure it. The method more specifically comprises disposing a photomask having a first shape between a first linear light irradiating source and a film-like structure and irradiating light from the irradiating source, and simultaneously therewith, disposing a second linear light irradiating source located opposite to the first light irradiating source with respect to the film-like structure, disposing a photomask having a second shape between the irradiating source and the film-like structure, and irradiating light from the second irradiating source.
Japanese Laid-Open Patent Publication No. 40903/1989 discloses a method of producing a light control plate as in the method disclosed in the above-cited patent document, which comprises dividing the surface of the film-like structure into a plurality of regions, irradiating light from a linear light irradiating source to at least one region, and to another region, (A) irradiating light from the linear light irradiating source at different angles from the above irradiating source, or (B) irradiating light from a point light source, or applying parallel light, or (C) irradiating diffused light, or (D) applying heat.
Japanese Laid-Open Patent Publication No. 77001/1989 discloses a light control plate composed of a plastic sheet which selectively diffuses incident light having a specific angle of incidence, and a method for its production.
In the above manufacturing method, a rod-like lamp is used as a light source. The resin plate which cures under light irradiation shows anisotropy in the long and short axes of the light source. Only when the resin plate is rotated with respect to the long axis direction of the light source, does it scatter light at a predetermined angle only when rotated in the long axis of the light source. Specifically, the resulting resin plate exists while a region having a different refractive index is oriented in a certain direction, and light which falls at a specific angle is considered to be diffused by this structure.
In the above light control plate, as described in the above patent document, part of the substrate plate is transparent at the front and is non-transparent when tilted to any side, with the remainder having a reverse function. There may be prepared a light control plate in which a first portion of the substrate plate is nontransparent when viewed from the front, a second portion is always non-transparent and the remainder is always transparent.
According to the method described in the above patent document, a photopolymerizable composition containing at least two compounds having at least one polymerizable carbon-carbon double bond in the molecules and having different refractive indices is maintained in a film form, and light is irradiated from a specific direction to cure it. A portion of the surface of the filmlike structure is divided into a plurality of areas by covering it with a photomask. Light from a first linear light irradiating source is irradiated to at least one of the areas, for example, that portion which faces the opening of the photomask, and light from a second linear light irradiating source is irradiated to at least one other area, for example, a portion covered by the photomask, at a different angle from that applied from the first irradiation source to perform curing. If after this, there is still an unirradiated portion, curing is completed by applying light or by polymerizing it with heat. As a result, there can be obtained a light control plate in which various regions having various different angles of diffusion are provided in the film-like structure.
Instead of the second linear light irradiating source, light from a point light source, on light from a parallel light source may be irradiated, or it is also possible to irradiate diffusing light or to apply heat. If point light or parallel light is irradiated, there was obtained a light control film wherein that portion which was cured later became uniformly like frosted glass and that portion which was cured by the first light source became angle dependent.
When diffused light is irradiated, there is obtained a light control film wherein only that portion which was cured by the first light source has angle-dependence and that portion which was cured later becomes transparent. According to the afore-mentioned method, a light control plate may be produced which has various regions having different ranges of scattering angles in a single resin plate.